Multi-ply paper bag with plastic liner of smaller dimension



E. S. NAYLOR June 13, 1967 MULTI-PLY PAPER BAG WITH PLASTIC LINER OF SMALLER DIMENSION 2 Sheets-Sheet 1 Filed July 21, 1965 INVENTOFE 7/ 12 TE TZ EDWARD QT'TOENEV June 13, 1967 E. s. NAYLOR 3,325,082

MULTIPLY PAPER BAG WITH PLASTIC LINER OF SMALLER DIMENSION 2 Sheets-Sheet 2 Filed July 21, 1965 wmwwwtlw Q M n F FILM E PHPER- PLASTIC SIZE DIFFERENTIAL IN PERCENT OF PLFJSTlC WIDTH INVENTOFE EDWARD S. NRYLOE av United States Patent 3,325 082 MULTI-PLY PAPER BAQ iiiliTH PLASTIC LINER 0F SMALLER DIMENSION Edward S. Naylor, Trenton, N .J., assignor to Union Camp Corporation, a corporation of Virginia Fiied July 21, 1965, Ser. No. 473,705 3 Claims. (Cl. 229- 55) This invention relates to new and useful improvements in multiple-ply paper bag structures. More particularly, the invention relates to a high strength, multiple-ply paper outer bag having a plastic liner in which the perimeter of the liner is from 49% less than the perimeter of the outer paper plies to enhance the strength of the plastic lined bag structure. The novel paper bags of the invention are of the type used in transporting such commodities as sugar, salt, fertilizers, chemicals, sand and various other materials.

Multiple-ply bags which are fully lined with plastic liners are Well-known and widely used. Two examples of prior art bag constructions may be seen in the US. patents to Geimer, No. 2,435,743, dated Feb. 10, 1948, for Waterproof Bag, and Doyle et al., No. 2,790,592, dated Apr. 30, 1957, for Laminated Material and Bags and Linings Made Therefrom.

In both of these prior art patents, the function of the synthetic thermoplastic liner material was for moisture resistance. However, in respect to the achievement of a mechanically strengthened structure to enable the sealed bag to be resistant to breakage, the present concept is wholly opposite to both the Geimer and Doyle patents since the 'liner width is critically less than the paper bag width.

Geimer, in Patent No. 2,435,743, conceives an inner flexible waterproof pillow-like bag the width and height of which are greater than the width and height of the outer supporting bag member, and the body of the inner bag is made relatively larger than the body of the outer supporting member in order to relieve the walls of the inner bag of all strains and stresses which might result from the bag being dropped or thrown. All of the weight r supporting function is thus provided in Geimer by the outer bag alone.

Doyle et al, also fold the liner to insure that the outer bag alone provides the Weight supporting function.

In contrast, the present invention relies upon the mechanical strength characteristics of the thermoplastic liner together with the mechanical strength characteristics of the multiple-ply outer bag structure having a liner height substantially equal to the outer multiple-ply paper bag but a liner perimeter critically smaller than the perimeter of the outer bag Within limits of 4 to 9%. A further requirement for the thermoplastic liner material is that it have elastic proper-ties which are defined by its ability to recover (a) at least (h) at least 72% of its tensile elongation after stretching 10% in a transverse direction. To illustrate, a polyethylene tubular liner, confined within a bag having outer paper plies, might stretch when the filled bag receives a sudden impact as by dropping and then recover quickly toward its original dimension.

At the present time there is no known standard method for determining the elastic recovery properties of various films within the ranges necessary for the present inven- 6 of its tensile energy and 1 tion. Consequently the inventor has devised a method for ascertaining the tensile-energy and tensile-elongation recovery of these films. Such method can be used to assure that films having the necessary properties are selected for the purpose herein.

A standard Instron Tester with automatic integrator and automatic cycling extension unit or any similar instrument which will perform the same functions, i.e. the measurement of the tensile, stretch and energy absorption at the desired conditions. The procedure is as follows:

(1) Cut film samples in transverse direction, 1" wide and of sufiicient length for ease of inserting sample in the jaws of the tester. An 8" gap was used but any other workable gap could be used.

(2) The return dial of the automatic cycling extension unit is set at 0.8" allowing for elongation of the film sample equal to 10% of the original length or jaw gap.

(3) The. crosshead speed is set at 20"/minute and chart speed at the same rate.

(4) The down button is depressed setting the lower jaw in motion, applying stress to the film thus elongating it to the predetermined level. When the jaws achieve 8.8" separation, the direction of travel is immediately reversed automatically and the lower jaw returns to its original position thereby relieving all the stress placed on the sample.

(5) The energy absorbed by the film in stretching is automatically recorded on the upper dial of the integrator and the energy released by the film as a result of stress relaxation is automatically recorded on the lower dial of the integrator.

(6) The stress-strain curve for this elongation is automatically recorded on the chart (FIG. 4) where A =area under stress portion=energy absorbed by film A =area under relaxed portion=energy released by film l =elongation under stress=l0% l =recovered elongation of film.

percent tensile-energy reeovery= X energy released energy absorbed X 100 integrator lower dial reading X100 integrator upper dial reading percent tensile-elongation reeovery=% 100 reoovered elongation stress elongation X100 linear measurement of Z linear measurement of l 100 The tensile-energy method requires only the direct reading of the integrator dials. The tensile-elongation 5 method requires linear measurements of Z and on the chart.

The tensile-elongation recovery levels of the films with which we are directly concerned are higher numerically than the tensile-energy recovery levels because of the property being measured but they are generally in relative alignment, i.e. when comparing films, the one with the highest tensile-energy recovery also possesses the highest tensile-elongation recovery. For example:

If these same films are subjected to automatic continuous cycling of stress application and relaxation as an extension of the elastic-recovery test, it is found that the films with the higher immediate elastic-recovery continue to display higher tensile-energy and tensile-elongation recovery and lower residual elongation even after 40 such cycles. Therefore, the measure of the immediate elastic-recovery of the film is indicative of the ability of the film to recover (released energy/ absorbed energy) from repeated stressing. The property of elastic recovery of a given film as described here exerts, in conjunction with paper-film dimensional spacing, a significant influence upon the performance of a paper-plastic bag in which construction the given film is used as a liner ply. Overall bag performance improves as films with higher elastic recoveries are utilized. The effect of the elastic recovery property upon paper-plastic bag performance is most pronounced when the optimum dimensional spacing between paper and film plies is employed.

The improved paper-plastic bag performance when compared to standard multiwall bag construction appears to be achiever through the combination of the elastic recovery of the film and the provision, through paperfilm dimensional difference, of space in which to permit the film to expand. The film will absorb energy during its expansion before coming in contact with the paper plies, thus relieving some of the stresses normally placed on the latter. The elastic recovery of the film then determines the ability of the film to continue to absorb energy and reduce the stresses upon the paper plies. Eventually, all films will display a decreasing ability to absorb energy and recover from repeated stresses but those films possessing the higher elastic recoveries will not reach this point as quickly as those with lower elastic recoveries, resulting in higher paper-plastic bag performance from the utilization of the former.

This property of high elastic recovery is exhibited by a number of thermoplastic films such as certain low density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, ethylene propylene copolymer, rubber hydrochloride, and ethylene butylene copolymer. This high elastic recovery property appears to be based upon the capacity of the plastic material to relieve strain without undergoing permanent deformation.

An example of a poor elastic recovery film material which would fail to meet the test is regenerated cellulose or cellophane. Parchmentized paper would also be unsatisfactory because it is not sufficiently elastic. Polystyrene plastic film would be unsatisfactory because of insuflicient recovery. Likewise it has been found that cellulose acetate, polyester film manufactured by the 4 Du Pont Company under the trademark Mylar, polyester fibre manufactured by the Du Pont Company under the trademark Dacron, vinyl chloride nylon, cellulose acetate and polybutadiene films would be unsatisfactory.

It appears, from a careful study of a large number of plastic liner materials tested extensively, that the expansion of the plastic liner due to internal stress must absorb shock energy due to certain characteristics inherent in the plastic material itself; e.g. the characteristics of resilience, tensile energy absorption and elastic recovery.

The present studies have disclosed that certain plastics fail in fatigue and are therefore unsatisfactory. The recovery is not rapid. Repeated blows, by drop test for example, cause failures.

It will thus be evident that it is an object of the invention to provide a bag in which the liner is related by critical dimensions to the outer bag structure and which exhibits certain elastic recovery properties.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises an article of manufacture possessing the features, properties, and the relation of elements which will be exemplified in the article hereinafter described and the scope of the invention which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:

FIGURE 1 is a perspective view of a two-ply tube with gussets embodying a liner in accordance with the invention and having the bottom closed with a sewn tape;

FIGURE 2 is a cut-away view of a two-ply tube without gussets embodying a liner in accordance with the invention and having the top closed with a sewn tape;

FIGURE 3 is a cross sectional view of the tube of FIGURE 1 showing the dimensional relationship of the liner to the other plies;

FIGURE 4 is a chart showing the stress-strain curve for the elongation of the film used in the liner; and

FIGURE 5 is a graph showing the effect of paperplastic size relationship upon progressive drop test performance.

Referring more particularly to the drawings there is shown in FIGURE 1 a tube 10 made of paper plies 11 and 12, forming the outer wall, and an inner plastic film liner 13. Such tube can be formed with gussets 14, as illustrated in FIGURE 1, or without gussets, as illustrated in FIG- URE 2. FIGURE 3 clearly shows that the perimeter of the liner is smaller than the perimeter of the outer wall. The relationship between such dimensions will be more fully specified hereinafter. FIGURES l and 2 show a sewn tape 15 as the closures for the tube, but it will be understood that any conventional closure, such as sewing, pasting, heat sealing, taping, or combinations thereof, may be used without affecting the advantages of the present invention.

Bags using different type films and with varying size relationships between the perimeter of the film liner and the perimeter of the paper outer wall were made up, filled with contents, closed and subjected to flat drop tests on alternate faces until the bags failed by having a break which caused the contents of the bag to leak out. The drop tests were conducted as follows: A bag was first dropped from a height of 24 inches. Drops were continued in increments of 6 inches in height up to 48 inches and thereafter in increments of 12 inches up to inches. If the bag had not failed up to that number of drops, drops were continued from 120 inches until failure. In the following performance tables the total cumulative inches of drops to failure are determined by adding together the number of inches of the drops.

The following table gives the safe inches of drop for various bag constructions with varying dimensional gaps between the film liner and outer plies for each bag construction:

Safe Inches of Drop With Following Size Dif- Bag Style Construcferentials tions 4 1. Flat sewn tube Film A 356 613 2, 564 2, 196 2. Flat sewn tube Film 13 573 942 1, 616 2, 073 1, 744 1, 793 3. Flat sewn tube Film C 418 603 l, 010 l, 593 1, 509 l, 550 4. Gusseted tube Film D 356 438 883 1, 149 5. Flat sewn tube Film E 236 497 627 661 Each bag had an outer wall made up of one ply of 50 1b. extensible multiwall paper and a second ply of 40 lb. extensible multiwall paper. In each case the film width (distance across face of bag) was held constant at 16 Inches and the width of the outer plies was adjusted to provide the size differential specified. The following films were used:

Film Al%'mil Ethylene-Vinyl Acetate Copolymer. Film B1 Inil Ethylene Vinyl Acetate Copolymer. Film C% mil low density Polyethylene. Film Dl% mil low density Polyethylene. Film E1V mil Ethylene Vinyl Acetate Oopolymer. These differentials in order represent dimensional differences in Width between the fihn ply and paper plies for this particular width of bag of 0, l, 1%, and 1% inches.

This relationship between the paper-plastic size differential (in percent of plastic width) and safe inches of drop for bags embodying different film liners is graphically illustrated in FIGURE 5. It will be noted that the most satisfactory results are obtained in a range where the plastic liner is between 4 and 9 percent smaller in cross dimension than the outer Wall. For the bag having a liner 16 inches in width the range in inches would be greater than /2 inch and less than 1 /2 inches.

Combining these results with the film characteristics heretofore explained it can be stated that bags of the present invention would give most satisfactory results where the following size differential and film properties were present:

Size ditferential4 to 9' percent smaller cross dimension for liner than outer plies;

Film energy recovery-at least 45 percent of its tensile energy after stretching 10% in the transverse direction;

Film elongation recoveryat least 72% of its tensile elongation after stretching 10% in the transverse direction.

The bags specified in the drop test table above were generally of a size adapted to hold 50 lbs. of product. In such tests on 50 lb. bags it has been found that the thickness of film can extend to mils. Of course, in bags of larger size such thickness might be increased. Economics and costs normally preclude the use of heavier gauge films as liners.

Although the foregoing tests and the drawings refer to a bag having two plies of paper and one ply of film, it should be understood that the same advantages of the present invention will result from a bag having one ply of paper or more than two plies of paper for the outer Wall. While the film liner provides a moisture barrier when necessary, it will be evident that such liner in the present invention furnishes additional strength rather than merely moisture resistance.

Since certain changes may be made in the above article, and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description (or shown in the accompanying drawing) shall 'be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A multiple-ply bag comprising: an outer tubular wall of at least one ply of paper; and an inner tubular liner of a thermoplastic film having a length substantially the same as the outer wall; said liner having a thickness of between 0.5 and 5.0 mils and a perimeter of from 4% to 9% less than the perimeter of the outer wall; said liner having elastic properties which, after stretching 10% in a transverse direction under stress, will recover at least 45% of its tensile energy and at least 72% of its tensile elongation.

2. The multiple-ply bag of claim 1 in which the outer wall comprises two plies of paper.

3. The multiple-ply bag of claim 1 in which the liner is selected from the group consisting of polyethylene, ethylene-vinyl acetate copolymer, polypropylene, ethylenepropylene copolymer, rubber hydrochloride, and ethylenebutylene copolymer.

References Cited UNITED STATES PATENTS 565,587 8/1896 Arkell 22955 1,723,255 8/1929 Rowe 229 -55 2,619,801 12/1952 Evans.

2,914,238 11/1959 Clark 22955 2,929,544 3/1960 Herschler 229 -55 3,190,441 6/1965 Rausing 229-55 X 3,248,040 4/ 1966 Friedman 22955 JOSEPH R. LECLAIR, Primary Examiner.

DAVIS T. MOORHEAD, Examiner. 

1. A MILTIPLE-PLY BAG COMPRISING: AN OUTER TUBULAR WALL OF AT LEAST ONE PLY OF PAPER; AND AN INNER TUBULAR LINER OF A THERMOPLASTIC FILM HAVING A LENGTH SUBSTANTIALLY THE SAME AS THE OUTER WALL; SAID LINER HAVING A THICKNESS OF BETWEEN 0.5 AND 5.0 MILS AND A PERMETER OF FROM 4% TO 9% LESS THAN THE PERIMETER OF THE OUTER WALL; SAID LINER HAVING ELASTIC PROPERTIES WHICH, AFTER STRETCHING 10% IN A TRANSVERSE DIRECTION UNDER STRESS, WILL RECOVER AT LEAST 45% OF ITS TENSILE ENERGY AND AT LEAST 72% OF ITS TENSILE ELONGATION. 